1. Field of Invention
The present invention relates to a propelling device for a projectile that is lying in a standby position within a rocket motor in a missile, where the projectile is translated in respect of the rocket motor by means of a pyrotechnic charge before the rocket motor is initiated.
2. Description of the Related Art
The propelling device according to the invention is developed for use in missiles, and in particular, but not exclusively, in rocket accelerated penetrators. Rocket accelerated penetrators are often kept in their storing and standby state with the main parts thereof not assembled. This means that the part having control fins, the fin cone, and the rocket motor proper is assembled to the penetrator at the moment before the missile is launched from the launcher. The penetrator, which is in form of an arrow like body having substantial mass, is lying in standby position in a translation tube within the rocket motor and with the pointed end thereof supported in the control fin part. How the assembly operation happens is described in detail in the priority founding Norwegian patent application no. 19992739.
During launching preparations the penetrator is translated through the translation tube and the control fin part, and the rear end of the penetrator is interlocked to the control fin part immediately before the rocket motor is ignited. It is common practise that the rocket motor is separated from the penetrator during the flight thereof as soon as the rocket motor is burned out and has lost its propelling force. It is the device for the forward propelling of the penetrator, and more generally the projectile, within the rocket motor until the rear end of the projectile locks to the rocket motor, the present application deals with.
According to the invention, a propelling device of the introductorily described kind is provided, which is distinguished in that the projectile is lying within a translation tube located centrally in the rocket motor, that the projectile comprises a power piston in the rear end thereof, that the power piston encloses a pyrotechnic igniter charge and a pyrotechnic squib and that the translation tube is sealingly closed behind the power piston and forms a closed expansion chamber for the pyrotechnic charges, which by ignition generates gas pressure that activates the power piston and thus the projectile.
In one embodiment the translation tube is sealingly closed behind the power piston by means of an end closure, which end closure is movable axially forward within the translation tube after the ignition of the pyrotechnic charges and translation of the power piston and the penetrator. At which moment of time the end closure moves forwards is dependent of the difference between the pressure in the chambre in the translation tube and the pressure that is generated within the rocket motor when initiated. The motional freedom of the end closure provides a possibility to balance this pressure differential. Thus fragmentation, collapse of or deformation of the translation tube during launching is avoided. At any costs, it is to be avoided that fragments from the inner parts of the rocket are getting into the nozzels of the rocket motor.
As a first alternative, the end closure is abutting an internal shoulder in the rear end of the translation tube.
As a second alternative, the end closure is abutting a perforated plate integrated to the rear end of the translation tube.
Preferably, a sealing means, such like an O-ring, can be provided between the end closure and the translation tube.
In one embodiment, the rear end of the projectile can be an integrated power piston that follows the projectile during the flight thereof
In a second embodiment, the power piston can be relesable from the projectile together with the rocket motor.
The propelling charge proper can be any suitable pyrotechnic charge, such like leadazide, BKNO3 or gunpowder and be in form of moulded pellets, granules or powder charge (pyrogenic igniter).
It is to be understood that the propelling device has completed its mission before the rocket motor is initiated and launched.